Temperature sensors are an integral part to many integrated circuits (“ICs”). Such sensors have applications ranging from optimizing computation speed in microprocessors to compensating for temperature dependency in high precision complex circuits.
For high precision temperature sensors and reference generations, typically, bipolar junction transistor (“BJT”) devices are used to implement such temperature sensors because of their superior characteristics over other types of transistors. However, BJT-based diodes have larger voltage-base-to-emitter (“VBE”) requirements and need more supply voltage head room. Hence, BJT-based temperature sensors can't be operated directly at low power voltage supply levels (e.g., at around 1V or sub-1V). Furthermore, in deep-submicron process technologies, parasitic variations can be significant in BJT-based temperature sensors. BJT-based temperature sensors can also have large process spread and may need additional mask layers for better control.
Operationally for BJT-based temperature sensors, a substantially similar amount of current is pumped into two BJT devices of different sizes to develop voltage differences Vb1 and Vb2, respectively, across each of the BJT devices. As widely known, voltage drop across a BJT device for a given current can be proportional to temperature. The two voltage drops across the two different BJT devices can then be used to solve for an unknown temperature value.
For the foregoing reasons, there is a need for new methods and apparatuses for temperature sensors for ICs that can accurately sense a wide range of temperatures and can also be operated at low power.